Ruminal motility of stocker cattle grazed on winter wheat pasture.

A 2-yr study was conducted to determine whether bloat of stocker cattle grazing winter wheat pasture is a primary bloat or a secondary bloat as a result of reduced ruminal motility. Amplitude (mm Hg) and frequency of ruminal contractions (contractions/min) of steers were measured before and after the steers were placed on wheat pasture, and at about weekly intervals during the pasture grazing periods. Implantable pressure transducers and water-filled balloon cannulas were used to measure ruminal motility. During the first year, amplitude of contractions increased (P less than .005) during grazing of wheat pasture (i.e., 20.5 vs 6.7 and 21.6 vs 12.9, respectively, for steers with implanted pressure transducers and water-filled balloon cannulas). Frequency of ruminal contractions of steers on wheat pasture was not decreased (P greater than .05). In the second year, amplitudes of ruminal contractions of steers on wheat pasture ranged from 11.0 to 33.5, and were either similar or greater (P less than .05) than the mean for the pre- and post-wheat pasture period (16.5). Frequencies of ruminal contractions that ranged from 1.66 to 1.80 were observed on four dates during the pasture grazing period, and were decreased (P less than .05) as compared with the mean for the pre- and post-wheat pasture period (2.43). However, the reduced frequencies were not accompanied by reduced (P greater than .05) amplitude x frequency of contractions. The data indicate that ruminal motility is not decreased in stocker cattle grazing winter wheat pasture.